For testing purposes I have to create a file with 1000 lines in it with one command.
What is a command to create a file on Linux?
touch is usually used to create empty files, but if you want to create a non-empty file, just redirect the output of some command to that file, like in the first line of this example:
$ echo hello world > greeting.txt
$ cat greeting.txt
hello world
A way to create a file with 1000 lines would be:
$ seq 1000 > file
for x in `seq 1 1000`; do echo "sometext" $x >>file.txt; done
you use the above for loop use print something $c times in text.txt.$c is number of runnning time (1,2,4...10000)
for (( c=1; c<=1000; c++ ));do echo "something $c times">>test.txt ;done
Related
When I execute the program in console I just do this:
./c1 2500
textfile.txt
and it just print a integer. The thing here is that I want to introduce 1000 textfiles as input so I made this script:
c=1
while [ $c -le 1000 ]
do
./c1 2500 >> sal.txt
$c.txt
(( c++ ))
done
The trouble here is that the script is not putting the output in the file text because is not iterating as it should, I think the problem is when the name of the filetext is introduced as $c.txt, how can i solve this?
Thanks for reading
$c.txt is not a command and the bash interpreter can't understand what that means
if you want to create a file, use touch [file]
or you want to copy a existing file to the destination, use cp [src_file] [dst_file]
so the code may like this:
./c1 2500 > $c.txt
or you may want to append the result to a file:
./c1 2500 > $c.txt
cat $c.txt >> sal.txt
ps:
> and >> both of these operators represent output redirection
> writes the output to the file
>> appends the output to the file
cat concatenates files and print on the standard output
I am trying to cat a file.txt and loop it twice through the whole content and copy it to a new file file_new.txt. The bash command I am using is as follows:
for i in {1..3}; do cat file.txt > file_new.txt; done
The above command is just giving me the same file contents as file.txt. Hence file_new.txt is also of the same size (1 GB).
Basically, if file.txt is a 1GB file, then I want file_new.txt to be a 2GB file, double the contents of file.txt. Please, can someone help here? Thank you.
Simply apply the redirection to the for loop as a whole:
for i in {1..3}; do cat file.txt; done > file_new.txt
The advantage of this over using >> (aside from not having to open and close the file multiple times) is that you needn't ensure that a preexisting output file is truncated first.
Note that the generalization of this approach is to use a group command ({ ...; ...; }) to apply redirections to multiple commands; e.g.:
$ { echo hi; echo there; } > out.txt; cat out.txt
hi
there
Given that whole files are being output, the cost of invoking cat for each repetition will probably not matter that much, but here's a robust way to invoke cat only once:[1]
# Create an array of repetitions of filename 'file' as needed.
files=(); for ((i=0; i<3; ++i)); do files[i]='file'; done
# Pass all repetitions *at once* as arguments to `cat`.
cat "${files[#]}" > file_new.txt
[1] Note that, hypothetically, you could run into your platform's command-line length limit, as reported by getconf ARG_MAX - given that on Linux that limit is 2,097,152 bytes (2MB) that's not likely, though.
You could use the append operator, >>, instead of >. Then adjust your loop count as needed to get the output size desired.
You should adjust your code so it is as follows:
for i in {1..3}; do cat file.txt >> file_new.txt; done
The >> operator appends data to a file rather than writing over it (>)
if file.txt is a 1GB file,
cat file.txt > file_new.txt
cat file.txt >> file_new.txt
The > operator will create file_new.txt(1GB),
The >> operator will append file_new.txt(2GB).
for i in {1..3}; do cat file.txt >> file_new.txt; done
This command will make file_new.txt(3GB),because for i in {1..3} will run three times.
As others have mentioned, you can use >> to append. But, you could also just invoke cat once and have it read the file 3 times. For instance:
n=3; cat $( yes file.txt | sed ${n}q ) > file_new.txt
Note that this solution exhibits a common anti-pattern and fails to properly quote the arguments, which will cause issues if the filename contains whitespace. See mklement's solution for a more robust solution.
I have an input file of this form:
Some text here
Another text here
Something else here
Now I want to write a linux script picks one line at a time from input file and creates a separate file which stores just the line received. After this I want to pass this file to a program (for which I have just binary file). Is it possible to write such a linux script. I am used to programming in C++ I know it is possible there. But I want to know if something like this is possible using linux script. Basically I intend to do the following:
read inputfile.txt line by line
store line read in inputFileInside.txt
./myprogram paramater1 inputFileInside.txt //run my C++ binary file which I usually run as (root$./myprogram parameter1 inputFileInside.txt)
sudo sh -c \"sync; echo 3 > /proc/sys/vm/drop_caches\"
exit when the input file has been read
you can read line by line like this using for loop
while read x
do
echo $x > inputFileInside.txt;
# do whatever you want
done < inputfile.txt
this may hep you to loop, $x is line read one by one till it reach end of file
while read x
do
echo $x > $2;
./myprogram paramater1
#your other command
done < $1;
save the above file as any name like prog.sh, then give execute permission and run ur program with argument
chmod u+x prog.sh
./prog.sh inputfile.txt inputFileInside.txt
here $1 is inputfile.txt and $2 is inputFileInside.txt
while read line; do
echo "$line" > inputFileInside.txt
./myprogram paramater1 inputFileInside.txt \
&& sudo sh -c \"sync; echo 3 > /proc/sys/vm/drop_caches\"
done < <(cat inputfile.txt)
This will:
input the file "inputfile.txt" line-by-line
each line will be assigned to $line as it is read
echo the line into "inputFileInside.txt" overwriting any previous information in it
run "./myprogram ..."
then only run "sudo ..." if "./myprogram ..." was successful
go to next line.
Make sure there is no white space (spaces) behind the end-of-line backslash (\).
I'm trying to write a pretty basic script in Linux shell but I'm still learning. Basically, everything is good to go except one part. I direct two outputs into the same file, e.g.:
echo `losetup -a` > partitionfile
echo "p1" >> partition final
Basically, I need to add the letter/number "p1" to the end of whatever is written in the file.
The problem is, it ends up being read (cat partitionfile) as:
/dev/loop0
p1
I need it on the same line to it reads out as:
/dev/loop0p1
There has to be a way to fix this, I just don't know it. Any help would be much appreciated!
Thanks!
I would go for:
echo "$(losetup -a)p1" > partitionfile
For an example, see the following transcript:
pax> echo "$(echo xyzzy_)p1"
xyzzy_p1
The xyzzy_ is the output of the inner echo command (which in your case would be losetup) and the outer echo command appends p1.
Hi Actually the correct option of echo to achieve this is "\c"
\c Keeps the cursor on the same line.
However you cannot use \c unless you have enabled it with
-e
Thus your code should be something like this ...
echo -e "`losetup -a` \c" > partitionfile
echo "p1" >> partition final
this will write in partitionfile as
< output of losetup -a > p1
everything on same line.
You can pass -n flag to the first echo statement to not print the trailing new line.
Ref: http://linux.die.net/man/1/echo
I have a text file, say, input.txt and I want to run a command and write the output to another text file, say, output.txt. I need to read values from input.txt, each value is in a line, then I need to insert them in the command then write the result in output.txt file. I tried the following and it works fine with me:
for i in `cat input.txt`; do command -m $i -b 100; echo $i; >> output.txt; done
Now, I need to make some improvements over this but I have little experience in Linux so I need some help.
What I need to do is:
1) Before each command result, I want to insert the value of i separated by comma. For example:
i1,result1
i2,result2
i3,result3
2) I need to change the second fixed value that I used in my command from a fixed value (100) to a value read from input.txt. So, the new input file which contains two values, say, newinput.txt is as the following:
i1,value1
i2,value2
i3,value3
Try this, in bash:
IFS=','
while read i val; do
echo -n "$i,"
command $i $val
done < input.txt > output.txt